1. Field of the Invention
The present invention relates generally to a sealing structure which includes a packing for sealing a sliding part of a valve for connecting together devices having a pressure differential between them and conveying powder particles such as, for example, a rotary valve or a reciprocating valve.
More particularly, the present invention relates to a sealing structure for sealing a sliding part with a packing which is formed by jointing together a member having a solid lubricating property and a member having substantial mechanical strength, wherein the member having the solid lubricating property is arranged forwardly in the direction in which the packing relatively moves, in order to permit the sliding part to be sealed positively over a wide range.
2. Description of the Prior Art
Generally, the sliding part of a valve to which the present invention is directed is sealed with a packing formed of rubber, nylon, ethylene tetrafluoride, or a soft metal, depending upon the conditions in which the valve is used, such as the temperature, pressure, and powder particle shape, with the packing being provided in the sliding part. However, the sealing means employing such conventional packing is not always satisfactory in its sealing effect, its durability, and the maintenance associated therewith. There are defects in a packing formed of such elastic material. Elastic material such as rubber or nylon, for example, is so low in mechanical strength that it is easily deformed and deterioration of mechanical properties of such material is likely to occur during extreme temperature conditions. Such elastic material is thus likely to have problems in its sealing effect and durability. A metal packing, on the other hand, is so high in frictional resistance as to seize on the sliding surface, and is thus remarkably worn by the damage imparted to the sliding surface. Such a metal packing requires repeated adjustment in response to such wear, and depending on the shape of the conveyed powder particles.
Another type of sealing means which has been employed includes a packing which is pushed out in response to the amount of wear by a solid lubricant being embedded in a metal base. However, such a packing is difficult to conform to the size, shape and material of the device with which it is being employed. Particularly, such a packing provides no appropriate sealing effect for a valve to be used under such conditions as high temperatures, high pressures, and powder particles entering the sliding part.